Applicants claim priority under 35 U.S.C. xc2xa7119 of German Application No. 103 06 907.0 filed Feb. 17, 2003.
1. Field of the Invention
The present invention relates to actuating drives for valve drives having a variably adjustable stroke, for actuating valves of internal combustion engines.
2. The Prior Art
Actuating drives in variable valve drives for an element that is to be pivoted, which determines the valve stroke with its angle position and is coupled with an actuating drive arranged lengthwise or crosswise to the crank shaft axis by way of toggle joints, are previously known. In these embodiments, a lever is always connected with the element that determines the valve stroke, in fixed rotational manner and axially guided, and can be pivoted together with this element.
The actuating drive has an actuating motor that drives a threaded spindle on which an actuating nut is arranged in fixed rotational manner, so as to be moved axially. In each case, one of the toggle joints is connected with the actuating nut in articulated manner, so as to pivot.
In this embodiment, with the actuating drive arranged crosswise to the crank shaft axis, the toggle joints are coupled by way of a rotational joint, while in the embodiment having an actuating drive arranged parallel to the crank shaft axis, the toggle joints are coupled by w ay of a ball joint. DE literature xe2x80x9cVariable Ventilsteuerungxe2x80x9d [Variable valve control]; Stefan Pischinger; expert-Verlag 2002; ISBN 3-8169-2119-1; p. 84, FIG. 6.
Because of the use of toggle joints that work together, such actuating drives take up a lot of room in the cylinder head.
It is therefore an object of the present invention to provide actuating drives for valve drives having a variably adjustable stroke, of the type described above, which can be arranged in cylinder heads having usual dimensions, next to the valve activation mechanisms, in an advantageous manner.
This object is achieved by an actuating drive wherein the element that is changeable in its angle position is provided with an actuating lever that is coupled in fixed rotational manner, which is in engagement with an actuating slide that is g sided to be displaced and pivoted in the cylinder head arranged adjacent to it. The actuating slide that can be displaced by an actuating motor has an actuating bridge on which the actuating lever rests on both sides and determines its angle position in its guidance in the cylinder head. These features, and their arrangement relative to one another provide an improved actuating drive.
In order to adjust the element that can be changed in terms of its angle position, the changeable element is provided with a guide toggle coupled in fixed rotational manner which, according to the invention, is in engagement with an actuating shaft arranged adjacent to it, guided in the cylinder head in displaceable manner.
This actuating slide has an actuating bridge in the region of the actuating path, with which contact surfaces of the actuating lever are engaged on one or both sides.
The actuating slide is coupled with an actuating motor, which effects the axial actuating movements of the slide counter to the forces introduced by the actuating lever. It is advantageous if the actuating slide is arranged on the side of the cylinder head opposite the camshaft, and it thereby fits advantageously into the usual design of cylinder heads.
It is advantageous if the control surface or control surfaces of the actuating bridge present on the actuating slide are designed so that the change in stroke decreases in proportion to the actuating path, when adjustments are made in the direction of the maximum stroke. This results in a more precise adjustment, on the one hand, and in a higher translation for the adjustment in the range of forces with a greater effect, in the case of a great or maximal valve stroke, on the other hand.
It is advantageous if the spring that engages on the intermediate member is supported on the changeable element. In this way, the force of the latter effects a torque or support moment in the direction of an adjustment towards a greater stroke, on the changeable element. With this spring arrangement, it is possible to reduce the required actuating forces.
Advantageous embodiments will be explained in the description below, in connection with their effects.